The present invention relates to an image sensing apparatus using a flash device and, more particularly to, an image sensing apparatus, such as an electronic camera, having an image sensing device.
It is necessary to use a flash device for sensing a low luminance object by an image sensing apparatus, such as an electronic camera. As a method of controlling a flash device, a method of causing the flash device to flash toward an object to be sensed with predetermined radiant quantities, and controlling radiant quantities on the basis of a quantity of reflected light from the object for sensing an image of the object has been suggested.
A conventional example is explained below.
FIG. 8 is a block diagram illustrating an image sensing system of a conventional electronic camera. In FIG. 8, reference numeral 601 denotes a focusing lens; 602, an image sensing device for converting incoming light into electric signals; 603, a signal processing circuit for generating a luminance signal and color signals from the electric signals generated by the image sensing device 602; 604, a photometry circuit for generating a photometric value of a scene on the basis of the luminance signal generated by the signal processing circuit 603; 606, a flash device for illuminating an object; and 605, a flash device controller for controlling radiant quantities of the flash device 606 using the photometric value generated by the photometry circuit 604.
In the conventional electronic camera as described above, light from the object incidents on the image sensing device 602 via the lens 601 and applied with photoelectric conversion by the image sensing device 602, and a video signal is generated by the signal processing circuit 603. Further, the photometric value is generated by the photometry circuit 604 on the basis of a luminance signal included in the video signal. According to a method, the flash device controller 605 controls the flash device 606 to flash, at least once, in known radiant quantities (called "pre-radiating operation", hereinafter) in advance of sensing an image.
The quantity of reflected light from the object in the pre-radiating operation is outputted as a photometric value from the photometry circuit 604, and the flash device controller 605 calculates radiant quantities which the object is properly illuminated in sensing the object on the basis of the photometric value obtained in the pre-radiating operation and controls the radiant quantities of the flash device 606. In this manner, it is possible to sense the object with proper exposure.
In the conventional image sensing apparatus as described above, in a case where center-weighted average photometry for performing photometry mainly on a central portion of a scene, for instance, is adopted as a photometry method, when a main object exists at a distance from the image sensing apparatus, a photometric value obtained by the photometry circuit sometimes results in a small value due to effects of dark areas around the main object. As a result, the main object would not be sensed with proper exposure.
Whereas, in a case where the photometry circuit performs peak photometry, when the distance to the object is long, it is possible to control the flash device so as to illuminate the object properly on the basis of a photometric value obtained by performing the peak photometry since, in the peak photometry, photometric values are obtained for a plurality of divided areas of a scene and the maximum photometric value among the photometric values is outputted from the photometry circuit. Therefore, the dark area around the object practically does not affect the peak photometry. However, when the distance between the image sensing apparatus and the object is short, since the radiant quantities of the flash device are controlled on the basis of the maximum photometric value in the divided areas of the scene in the peak photometry, the object may not be sensed with proper exposure.